This invention generally relates to vehicle suspension systems. More particularly, this invention relates to a system for stabilizing a suspension system under selected conditions.
A variety of suspension systems are available for passenger and heavy duty vehicles. One type of suspension provided for heavy duty vehicles is air-based and includes the ability to adjust the position of an axle on a truck trailer. These suspensions are particularly useful for truck trailers that are optionally made into trains and transported by railway. When such a truck trailer is utilized for driving along the highway, for example, the suspension is adjusted into a first position where the wheels are spaced from the underside of the trailer a sufficient distance for driving along the road. When the trailer is to be transported by train, however, the suspension is adjusted so that the wheels are in a relatively retracted position, closer to the underside of the trailer. Since the wheels need to be adjusted into the two different positions, the suspension system must be adjustable to accommodate movement of the wheel axle between the two positions.
While such systems have proven useful and advantageous, they are not without shortcomings and drawbacks. For example, since the suspension system must accommodate movement of the axle between two relatively extreme positions, there is a requirement for a large amount of resiliency in the suspension system. This resiliency can pose problems under certain conditions.
For example, when loading a trailer, it is common to drive a lift truck onto the trailer bed. Because the lift truck is typically very heavy, a large load is rapidly imposed on the suspension system, which cannot react quick enough to avoid having the trailer bed drop suddenly as a result of the weight of the lift truck. This poses at least two problems. First, this provides undesirable wear on the trailer suspension components. Second, when the trailer is at a docking station, for example, it is necessary to maintain the truck bed at a height that enables a worker to easily move between the truck bed and the loading dock. When the truck bed drops because the air-based suspension system cannot accommodate the weight of a lift truck, for example, it may not be possible to drive the lift truck off of the trailer bed back onto the loading dock. In some instances, the air-based suspension system is not capable of being adjusted sufficient to raise the trailer bed back to a height consistent with the loading dock.
Additionally, when a lift truck is driven off of a trailer bed, the trailer bed often bounces upward in response to the force that is provided by the air-based suspension system, which has been under high pressure in an attempt to counteract the weight of the lift truck. Since the suspension system is provided with enough air to support the weight of the lift truck, when the lift truck leaves the trailer bed, the system is not able to adjust quickly enough to avoid the trailer bed being bounced upward. This undesirably increases the wear on the suspension components and can pose problems to the cargo that is loaded onto the trailer bed.
Therefore, there is a need for an improved suspension system that can be stabilized to avoid the shortcomings and drawbacks discussed above while still permitting the suspension system to be adjusted into the positions necessary to accommodate driving along a highway or being transported by railway. This invention addresses those needs by providing an improved suspension system.